The present invention relates to an arm head of a wiper arm.
A typical wiper arm includes an arm head and a retainer. The arm head includes a distal portion with respect to the longitudinal direction. A coupling bore extends through the distal portion in a direction orthogonal to the longitudinal direction. The retainer is coupled to the arm head and is pivotal about a shaft inserted through the coupling bore. An anti-glare and rust resistant coating is applied to the wiper arm to prevent light reflection and metal corrosion.
The retainer is formed by bending a steel plate into a U-shape. After bending the steel plate, it is difficult to coat the inner side of the retainer. Thus, for example, one side of the steel plate is coated in advance. In this case, the steel plate is bent so that the coated surface is arranged at the inner side. Then, the outer side of the steel plate is coated so that the retainer is entirely coated to prevent metal corrosion (refer to, for example, Japanese National Phase Laid-Open Patent Publication No. 2007-501152).
The coupling bore of the arm head receives the shaft. Thus, the coating is not applied to the wall of the coupling bore. For example, as shown in FIG. 14, an arm head 101 includes a coupling bore 102, and a coating 103 is applied to the arm head 101 but not to the wall of the coupling bore 102. In this case, a corrosion product 104 may form inside the coating 103 on the arm head 101 near the open end of the coupling bore 102. As corrosion advances, the corrosion product 104 may expand or separate the coating 103. Such a corroded portion would stand out and adversely affect the outer appearance of the arm head prematurely.